Printing systems form images on image receiving members including paper and other print media. Different printing techniques including laser printing, inkjet printing, offset printing, dye-sublimation printing, thermal printing, and the like may be used to produce printed documents. In particular, inkjet imaging devices eject liquid ink from printheads to form images on an image receiving member. The printheads include a plurality of inkjets that are arranged in some type of array. Each inkjet has a thermal or piezoelectric actuator that is coupled to a printhead controller. The printhead controller generates firing signals that correspond to digital data for images. The frequency and amplitude of the firing signals correspond to the selective activation of the printhead actuators. The printhead actuators respond to the firing signals by ejecting ink drops onto an image receiving member to form an ink image that corresponds to the digital image used to generate the firing signals.
Throughout the life cycle of printing systems, the image generating ability of the system requires evaluation and, if the images contain detectable defects, correction. Various defects in the image generating process affect ink image quality. These defects include transient defects that occur during a printing process for a comparatively short time period. While various techniques exist to measure image quality and detect defects, the transient defects may change too quickly for the existing techniques to detect the defects effectively and enable the printing system to take corrective actions. For example, image quality defects are often detected by printing known test patterns on a print medium and analyzing the test patterns for image defects. Typical test patterns include one or more predefined shapes such as lines, dashes, and geometric figures, contone or halftoned areas that enable a printer to detect image defects and to calibrate one or more components to correct the defects. These test patterns present several disadvantages since they consume print media that could otherwise be used for printing images, and since they must be separated from the printed customer prints during or after the print job. Additionally, transient defects may occur between printing test patterns and avoid detection in the test pattern image data. Being able to detect transient image quality defects from customer generated images without requiring predetermined test patterns or knowledge of the image content would be useful.